US20150177298A1 - Capacitive sensor electrode - Google Patents

Capacitive sensor electrode Download PDF

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Publication number
US20150177298A1
US20150177298A1 US14/558,858 US201414558858A US2015177298A1 US 20150177298 A1 US20150177298 A1 US 20150177298A1 US 201414558858 A US201414558858 A US 201414558858A US 2015177298 A1 US2015177298 A1 US 2015177298A1
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electrode
capacitive sensor
transmission
reception
sensor electrode
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Takehiko Sugiura
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Aisin Corp
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Aisin Seiki Co Ltd
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/044—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by capacitive means
    • G06F3/0448—Details of the electrode shape, e.g. for enhancing the detection of touches, for generating specific electric field shapes, for enhancing display quality
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
    • G01R27/2605—Measuring capacitance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/003—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring position, not involving coordinate determination

Definitions

  • This disclosure relates to a capacitive sensor electrode.
  • a capacitive sensor that detects a position or a motion of a detection object from a change in capacitance.
  • the capacitive sensor includes one or plural detection electrodes. Capacitance values of the electrodes change along with an approach or a movement of a detection object. The capacitive sensor measures this change in capacitance value as an electric signal to detect the motion of the detection object.
  • a capacitive sensor is widely used as, for example, a non-contact object detector or a display touch panel.
  • JP 2012-203901A discloses a capacitive sensor which is used in a display with a touch sensor.
  • This capacitive sensor includes plural signal lines Tx and plural signal lines Rx crossing each other, and capacitances are formed between the signal lines Tx and the signal lines Rx.
  • a voltage is applied between the signal lines Tx and the signal lines Rx, an electric field is generated between the signal lines Tx and the signal lines Rx.
  • this electric field is interrupted by a finger of an operator, the amount of charge accumulated between the signal lines Tx and the signal lines Rx decreases.
  • the capacitive sensor detects an approach of a finger, that is, an approach of a finger to the display.
  • Such a capacitive sensor measures a change in mutual capacitances formed between the signal lines Tx and the signal lines Rx and thus is called a mutual capacitance type.
  • the mutual capacitance type capacitive sensor disclosed in Reference 1 detects a change in capacitance when an electric field between the signal lines Tx and the signal lines Rx is interrupted, for example, as illustrated in FIGS. 1A and 1B of Reference 1.
  • An electric field generated from the signal lines Tx is concentrated between the signal lines Tx and the signal lines Rx. Accordingly, when a change in capacitance is detected, the position of a detection object is specified to be near a position immediately above a gap between the lines Tx and Rx.
  • the mutual capacitance type capacitive sensor has a detection range limited to a predetermined direction or range and thus is excellent in directivity.
  • the detection sensitivity rapidly decreases along with an increase in the distance between the sensor and a detection object. Therefore, it is difficult to use the mutual capacitance type capacitive sensor for a sensor distant from a detection object, for example, a vehicle proximity sensor, due to its insufficient detection sensitivity.
  • An aspect of this disclosure provides a capacitive sensor electrode including: a first electrode that is disposed on a principal surface of a substrate; and a second electrode that is disposed on the principal surface to be distant from the first electrodes, in which the first electrode has a shape so as to be positioned on opposite sides of the second electrode.
  • FIG. 1A is a perspective view illustrating a capacitive sensor electrode according to a first embodiment disclosed here;
  • FIG. 1B is a plan view illustrating the capacitive sensor electrode according to the first embodiment disclosed here;
  • FIG. 1C is a cross-sectional view taken along IC-IC line illustrating the capacitive sensor electrode according to the first embodiment disclosed here;
  • FIG. 2 is a cross-sectional view illustrating the capacitive sensor electrode according to the first embodiment disclosed here and a diagram illustrating drive circuits of a capacitive sensor;
  • FIG. 3 is a schematic diagram illustrating a distribution of electric force lines when a voltage is applied to the capacitive sensor electrode according to the first embodiment disclosed here;
  • FIG. 4 is a schematic diagram illustrating a change in the electric force lines when a detection object approaches the capacitive sensor electrode according to the first embodiment disclosed here;
  • FIG. 5 is a diagram illustrating a modification example of drive circuits used in the capacitive sensor electrode according to the first embodiment disclosed here;
  • FIG. 6A is a plan view illustrating a capacitive sensor electrode having a transmission/reception structure
  • FIG. 6B is a plan view illustrating a capacitive sensor electrode having a transmission/reception/transmission structure
  • FIG. 7 is a graph illustrating experiment results which indicate a difference in detection sensitivity between the transmission/reception structure and the transmission/reception/transmission structure
  • FIG. 8A is a cross-sectional view illustrating the capacitive sensor electrode having a transmission/reception structure in the width direction and is a graph illustrating the detection sensitivity of a capacitive sensor;
  • FIG. 8B is a cross-sectional view illustrating the capacitive sensor electrode having a transmission/reception/transmission structure in the width direction and is a graph illustrating the detection sensitivity of a capacitive sensor;
  • FIG. 9 is a graph illustrating experiment results which indicate a variation in detection sensitivity depending on a ratio of the widths of transmission electrodes and a reception electrode;
  • FIG. 10A is a schematic diagram illustrating a capacitive sensor electrode in which a reception electrode has an elliptical shape
  • FIG. 10B is a schematic diagram illustrating a capacitive sensor electrode in which a reception electrode has a perfectly circular shape
  • FIG. 10C is a schematic diagram illustrating a capacitive sensor electrode in which a reception electrode has a rectangular shape
  • FIG. 11 is a graph illustrating simulation results which indicate a variation in detection sensitivity depending on the shapes of capacitive sensor electrodes
  • FIG. 12 is a diagram illustrating the shape of a Lame curve (superellipse).
  • FIG. 13 is a diagram illustrating a capacitive sensor electrode in which the outer shape of a transmission electrode is rectangular and the outer shape of a reception electrode is elliptical;
  • FIG. 14 is a cross-sectional view illustrating a capacitive sensor electrode according to a third embodiment disclosed here.
  • FIG. 15 is a plan view illustrating a capacitive sensor electrode according to a fourth embodiment disclosed here.
  • FIGS. 1A , 1 B, and 1 C illustrate a structure of a capacitive sensor electrode according to a first embodiment disclosed here.
  • FIG. 1A is a perspective view of the capacitive sensor electrode
  • FIG. 1B is a plan view of the capacitive sensor electrode
  • FIG. 10 is a cross-sectional view taken along IC-IC line of FIG. 1B .
  • a capacitive sensor electrode 100 includes a transmission electrode 102 as a first electrode and a reception electrode 103 as a second electrode that are disposed on a principal surface of a substrate 101 .
  • the substrate 101 is an insulating substrate and may be formed of, for example, a resin or a glass.
  • the transmission electrode 102 and the reception electrode 103 are disposed on the same principal surface of the substrate 101 .
  • the transmission electrode 102 and the reception electrode 103 are formed of, for example, conductive metal.
  • the substrate 101 is not particularly limited as long as it includes a surface on which the capacitive sensor electrode is formed, and may not be a plate shape.
  • An outer periphery of the reception electrode 103 has an elliptical shape.
  • the transmission electrode 102 has a ring shape having an inner periphery and an outer periphery and is disposed so as to surround the reception electrode 103 with a gap 104 interposed between the transmission electrode 102 and the reception electrode 103 . That is, the gap 104 is formed as a ring-shaped trimmed pattern between the transmission electrode 102 and the reception electrode 103 .
  • An outer periphery of the transmission electrode 102 has an elliptical shape.
  • a long axis of the elliptical shape forming the outer periphery of the transmission electrode 102 and a long axis of the elliptical shape forming the outer periphery of the reception electrode 103 have a position relationship of being perpendicular to each other.
  • the transmission electrode 102 is positioned on opposite sides of the reception electrode 103 with the gap 104 interposed between the transmission electrode 102 and the reception electrode 103 .
  • the sizes of the long axis and the short axis of the transmission electrode 102 are 100 mm and 60 mm, respectively, and the sizes of the long axis and the short axis of the reception electrode 103 are 50 mm and 30 mm, respectively.
  • the capacitive sensor electrode 100 may further include an insulating film for covering at least a part of the transmission electrode 102 and the reception electrode 103 . By providing the insulating film, deterioration such as corrosion of the transmission electrode 102 and the reception electrode 103 are prevented.
  • FIG. 2 is a cross-sectional view illustrating the capacitive sensor electrode according to the first embodiment disclosed here and a diagram illustrating drive circuits of a capacitive sensor using the capacitive sensor electrode.
  • a voltage control section 210 and a capacitance detecting section 220 as the drive circuits are connected to the capacitive sensor electrode 100 through wiring.
  • the voltage control section 210 includes a power supply 211 , a switch 212 , and a sensor control unit 213 .
  • the power supply 211 supplies a DC voltage.
  • the switch 212 is connected between the transmission electrode 102 of the capacitive sensor electrode 100 and the power supply 211 .
  • the switch 212 switches between ON (connection) and OFF (disconnection) of the supply of voltage to the transmission electrode 102 based on a control signal of the sensor control unit 213 .
  • a DC voltage is supplied from the power supply 211 to the transmission electrode 102 .
  • the switch 212 is switched to OFF, the transmission electrode 102 is connected to the ground, and charge accumulated on the transmission electrode 102 is released.
  • the sensor control unit 213 is not particularly limited as long as it has a function of transmitting a signal of controlling the switch 212 , and this function can be implemented by a software program or by a hardware element such as an IC (not illustrated) for driving the capacitive sensor electrode 100 .
  • the voltage supplied from the power supply 211 is positive. However, the voltage may be negative, and in this case, directions of electric force lines in the drawing are reversed.
  • the capacitance detecting section 220 includes a comparator 221 , a reference capacitance 222 , a reference power supply 223 , and a detecting unit 224 .
  • the comparator 221 includes a non-inverting input terminal, an inverting input terminal, and an output terminal.
  • the inverting input terminal of the comparator 221 is connected to the reception electrode 103 and the reference capacitance 222 .
  • FIG. 2 only the above-described three terminals are illustrated, but actually, the comparator 221 further includes one or more power terminals (not illustrated).
  • the reference capacitance 222 is connected between the inverting input terminal of the comparator 221 and the ground.
  • the reference capacitance 222 divides the power supply voltage together with a capacitance between the transmission electrode 102 and the reception electrode 103 . Accordingly, the capacitance value of the reference capacitance 222 is preferably set to be the same as the capacitance value between the transmission electrode 102 and the reception electrode 103 .
  • the reference power supply 223 is connected between the non-inverting input terminal of the comparator 221 and the ground.
  • the voltage of the reference power supply 223 is a reference voltage for comparing to the voltage of the reception electrode, and thus a voltage value is preferably set to be, for example, about 1 ⁇ 2 of the voltage of the power supply 211 .
  • the voltage of the reference power supply 223 may be supplied from the same power supply device by dividing the voltage of the power supply 211 or may be supplied from another power supply device having a different voltage.
  • the detecting unit 224 is connected to the output terminal of the comparator 221 .
  • the detecting unit 224 measures an output voltage of the comparator 221 and, based on this voltage value, determines whether or not an object which changes the capacitance between the transmission electrode 102 and the reception electrode 103 is present near the capacitive sensor electrode 100 .
  • the detecting unit 224 is not particularly limited as long as it has functions of: measuring an output voltage of the comparator 221 ; and, based on this output voltage, transmitting a control signal to another device. This function can be implemented by a software program or by a hardware element such as an IC (not illustrated).
  • FIG. 3 is a schematic diagram illustrating a distribution of electric force lines during voltage application.
  • the switch 212 is switched to ON, the voltage of the power supply 211 is applied to the transmission electrode 102 , and electric force lines moving from the transmission electrode 102 to the reception electrode 103 are generated.
  • FIG. 4 is a schematic diagram illustrating a change in the electric force lines when a detection object approaches the capacitive sensor electrode.
  • a detection object 401 approaches a position near the capacitive sensor electrode 100
  • some of the electric force lines moving from the transmission electrode 102 to the reception electrode 103 move to the detection object 401 . Accordingly, the number of electric force lines received in the reception electrode 103 decreases.
  • a voltage value supplied from the power supply 211 to the transmission electrode 102 is set as Vdd.
  • Vdd voltage value supplied from the power supply 211 to the transmission electrode 102
  • a capacitance is formed between the transmission electrode 102 and the reception electrode 103 .
  • a capacitance value of this capacitance is set as Cs.
  • the reception electrode 103 is connected to the ground through the reference capacitance 222 of the capacitance detecting section 220 .
  • a capacitance value of the reference capacitance 222 is set as Cref.
  • a voltage input to the non-inverting input terminal of the comparator 221 is a voltage of the reference power supply 223 . This voltage is set as Vref.
  • the comparator 221 outputs a high-level or low-level voltage signal to the detecting unit 224 , the voltage signal indicating a magnitude relation of the capacitance between the transmission electrode 102 and the reception electrode 103 and the reference capacitance 222 .
  • Cs is set to satisfy Cs>Cref.
  • a low-level voltage is input to the detecting unit 224 .
  • the detection object 401 approaches the capacitive sensor electrode 100 , electric force lines between the transmission electrode 102 and the reception electrode 103 are interrupted, and the capacitance Cs decreases.
  • the voltage input to the detecting unit 224 changes from a low level to a high level. By detecting this change in voltage level, the approach of the detection object 401 can be detected.
  • the capacitive sensor electrode 100 according to the first embodiment disclosed here can be adopted for a mutual capacitance type capacitive sensor which detects a change in capacitance when electric force lines generated between the transmission electrode 102 and the reception electrode 103 are interrupted. Since the mutual capacitance type is adopted, an electric field is concentrated in the vicinity of the gap 104 . Accordingly, the detection object 401 is detected when being near the gap 104 . Accordingly, when a large object is present at a position distant from the capacitive sensor electrode 100 , erroneous detection does not occur. For example, it is not determined that a small object is detected near the gap 104 .
  • a property in which the detection range is limited to a predetermined direction or range as described above is expressed by “the detection sensitivity being excellent in directivity”.
  • the comparator circuit using the comparator 221 has been described as an example. However, other circuits may be used as long as they can measure a change in the capacitance between the transmission electrode 102 and the reception electrode 103 .
  • a circuit including a negative feedback unit such as a voltage follower circuit using a differential amplifier 521 as illustrated in FIG. 5 may be used.
  • a non-inverting input terminal is connected to the reception electrode 103
  • an inverting input terminal is connected to an output terminal.
  • a voltage signal input to the detecting unit 224 is not binary data containing a high-level value and a low-level value but analog data containing continuous values. Accordingly, a change in the capacitance between the transmission electrode 102 and the reception electrode 103 can be detected in more detail as compared to the case of the binary data.
  • an AD converter may be disposed in a stage after the output terminal of the comparator 221 so as to convert a voltage signal to digital data suitable for signal processing.
  • a voltage amplifying circuit may be adopted instead of the voltage follower circuit.
  • FIGS. 6A and 6B are diagrams illustrating experiment results of comparing a structure in which a transmission electrode and a reception electrode are disposed in parallel and a structure in which a transmission electrode is disposed on opposite sides of a reception electrode.
  • FIG. 6A is a plan view illustrating a capacitive sensor electrode 600 a .
  • a transmission electrode 602 a and a reception electrode 603 a are disposed in parallel with a gap 604 a interposed between the transmission electrode 602 a and the reception electrode 603 a (hereinafter, this structure will be referred to as “transmission/reception structure”).
  • FIG. 6B is a plan view illustrating a capacitive sensor electrode 600 b for comparison to FIG. 6A .
  • Transmission electrodes 602 b are disposed so as to surround a reception electrode 603 b with gaps 604 b interposed between the respective transmission electrodes 602 b and the reception electrode 603 b (hereinafter, this structure will be referred to as “transmission/reception/transmission structure”).
  • These capacitive sensor electrodes 600 a and 600 b were prepared to perform an experiment of measuring a change in capacitance when an detection object approaches each of the capacitive sensor electrodes 600 a and 600 b .
  • the structures of the electrodes are simplified to be rectangular as illustrated in the drawings instead of being elliptical as in the first embodiment disclosed here.
  • FIG. 7 is a graph illustrating experiment results which indicate a difference in detection sensitivity between the transmission/reception structure and the transmission/reception/transmission structure.
  • the horizontal axis represents the distance (mm) between the capacitive sensor electrodes 600 a and 600 b and the detection object
  • the vertical axis represents a capacitance change amount (arbitrary unit) when the detection object approaches the capacitive sensor electrodes 600 a and 600 b .
  • the reason for expressing the capacitance change amount by an arbitrary unit is that capacitance data acquired from a capacitance measuring device is based on a unique parameter of the device and cannot be converted into a general unit system such as SI.
  • FIGS. 8A and 8B are schematic diagrams illustrating a difference in detection sensitivity between the transmission/reception structure and the transmission/reception/transmission structure.
  • FIG. 8A is a cross-sectional view illustrating the capacitive sensor electrode 600 a having a transmission/reception structure of FIG. 6A in the width direction and is a graph illustrating the detection sensitivity of the capacitive sensor electrode 600 a at each position of the width direction.
  • the sensitivity of a position near the gap 604 a between the transmission electrode 602 a and the reception electrode 603 a is the highest. Accordingly, it is considered that the graph is plotted in a bell shape in which the detection sensitivity has a peak near the gap 604 a.
  • FIG. 8B illustrates the detection sensitivity of the capacitive sensor having a transmission/reception/transmission structure contrary to the above detection sensitivity.
  • the description of the drawing and the graph are the same as those in FIG. 8A and thus will not be repeated.
  • the sensitivity of positions near the gaps 604 b between the respective transmission electrodes 602 b and the reception electrode 603 b is also the highest.
  • peaks of the detection sensitivity strengthen each other. Accordingly, it is considered that the detection range also increases along with the improvement of the detection sensitivity.
  • the capacitance change amount of the transmission/reception/transmission structure is greater in the experiment results of FIG. 7 .
  • the reception sensitivity of a capacitive sensor is improved by adopting the transmission/reception/transmission structure, that is, the structure in which transmission electrodes surround a reception electrode with gaps interposed between the respective transmission electrodes and the reception electrode.
  • the peak intensity and the range of the detection sensitivity can be adjusted by adjusting the distance between the two gaps.
  • the distance between the gaps is narrowed, the peaks strengthen each other, and the detection sensitivity is further improved.
  • the detection sensitivity decreases, but the detection range is further widened. In this way, a relationship between the detection sensitivity and the detection range can be adjusted by distance between the gaps.
  • the distance between the gaps is determined by the width of the reception electrode 603 b . Therefore, experiment results of investigating the width of a reception electrode will be described.
  • FIG. 9 is a graph illustrating experiment results which indicate a variation in detection sensitivity depending on a ratio of the areas of transmission electrodes and a reception electrode.
  • the horizontal axis represents the distance (mm) between a sensor and a detection object
  • the vertical axis represents a capacitance change amount (arbitrary unit) when the detection object approaches the sensor.
  • area of transmission electrodes represents the total area of transmission electrodes surrounding a reception electrode.
  • the capacitance change amount is about 2 times that of a case where the area ratio is 1:1.
  • the area ratio of the transmission electrodes is more than 4:1, the capacitance change amount tends to decrease.
  • the area ratio of the transmission electrodes to the reception electrode is particularly preferably within a range of 2:1 to 4:1.
  • the reason why the above results are obtained is considered to be as follows.
  • the area of the transmission electrodes increases, electric force lines generated from the transmission electrodes are distributed in a wide range.
  • the area of the reception electrode excessively decreases, the number of electric force lines which can be received in the reception electrode decreases.
  • the structure of the capacitive sensor electrode had the same transmission/reception/transmission structure as that illustrated in FIG. 6B , and in a state where the total size thereof was fixed to 100 mm ⁇ 60 mm, the area ratio of the transmission electrodes to the reception electrode was changed.
  • the distance between the capacitive sensor electrode and the detection object was 80 mm.
  • FIGS. 10A , 10 B, and 10 C are plan views schematically illustrating the shapes of electrodes which are targets of the simulation. These diagrams are conceptual diagrams for illustrating the shapes of the electrodes and are not the same as actual simulation models.
  • FIG. 10A is a schematic diagram illustrating the shape of a capacitive sensor electrode model 1000 a in which a reception electrode 1003 a has an elliptical shape.
  • the reception electrode 1003 a has an elliptical shape.
  • a transmission electrode 1002 a has a hollow shape and is disposed so as to surround the reception electrode 1003 a with a gap 1004 a interposed between the transmission electrode 1002 a and the reception electrode 1003 a .
  • An outer periphery of the transmission electrode 1002 a has an elliptical shape.
  • a ground electrode 1001 is disposed on the outside of the transmission electrode 1002 a with a gap 1005 interposed between the transmission electrode 1002 a and the ground electrode 1001 .
  • the ground electrode 1001 is provided in consideration of an influence of, for example, a case where a metal member, which may be present near the capacitive sensor electrode 1000 a when the capacitive sensor electrode 1000 a is actually installed, acts as the ground.
  • the ground electrode 1001 may be disposed on the outer periphery of the capacitive sensor electrode 1000 a to reduce an error caused by ground wiring or the like which may be present near the capacitive sensor electrode 1000 a.
  • FIG. 10B is a schematic diagram illustrating the shape of a capacitive sensor electrode model 1000 b in which a reception electrode 1003 b has a perfectly circular shape.
  • FIG. 10C is a schematic diagram illustrating the shape of a capacitive sensor electrode model 1000 c in which a reception electrode 1003 c has a rectangular shape. Since the configurations other than the shape of each of the electrodes are the same as those of the capacitive sensor electrode model 1000 a illustrated in FIG. 10A , the detailed description thereof will not be repeated.
  • FIG. 11 is a graph illustrating simulation results which indicate a variation in detection sensitivity depending on the shapes of the capacitive sensor electrodes illustrated in FIGS. 10A , 10 B, and 10 C.
  • the horizontal axis represents the distance (mm) between a sensor and a detection object
  • the vertical axis represents a capacitance change amount (arbitrary unit) when the detection object approaches the sensor.
  • a solid-line graph represents the results of the case where the reception electrode has an elliptical shape as illustrated in FIG. 10A
  • a broken-line graph represents the results of the case where the reception electrode has a perfectly circular shape as illustrated in FIG. 10B .
  • unique error factors of the simulation are excluded therefrom.
  • the capacitance change amount data is corrected by subtracting measurement data of the case of FIG. 10C where the reception electrode has a rectangular shape therefrom. That is, in this graph, data is plotted as a relative comparative value when the value of the case where the reception electrode has a rectangular shape is set to reference (zero). Accordingly, when a value of each graph is positive, a change in capacitance when the detection object approaches the capacitive sensor electrode is larger, and the sensitivity of the capacitive sensor is higher as compared to the case where the reception electrode has a rectangular shape. It can be understood from the above results that, in either case where the reception electrode has an elliptical shape or a perfectly circular shape, a capacitance change amount is larger than that of the case where the reception electrode has a rectangular shape.
  • the gap between the transmission electrode and the reception electrode is linear. Therefore, electric force lines to be generated are substantially parallel to each other and are not likely to be concentrated.
  • the gap between the transmission electrode and the reception electrode is arc-shaped or curved. Therefore, electric force lines are more likely to be concentrated as compared to the case where the reception electrode has a rectangular shape.
  • the reception electrode it is considered that a capacitance change amount increases when the detection object approaches the capacitive sensor electrode.
  • the reception electrode it is more preferable that the reception electrode have an elliptical shape or a perfectly circular shape having an arc-shaped or curved end portion.
  • the shape of an ellipse is determined by two parameters including the length of a long axis and the length of a short axis.
  • the shape of a perfect circle is determined by only one parameter of a radius (or a diameter).
  • an area ratio of a transmission electrode to a reception electrode is one of the parameters which determine the detection sensitivity of a capacitive sensor.
  • a perfectly circular electrode has a low degree of freedom for design because the width thereof cannot be changed at a fixed area.
  • an elliptical electrode has a high degree of freedom for design because the width thereof can be changed at a fixed area by changing a ratio of the length of a long axis to the length of a short axis. Accordingly, it is preferable that a reception electrode has an elliptical shape.
  • an electrode shape may be a Lame curve (superellipse) represented by the following expression (1) which is a generalized figure of a circle, an ellipse, a rectangle, a rhombus, and the like.
  • the Lame curve is a rhombus.
  • the Lame curve is an ellipse.
  • the Lame curve is a perfectly circular shape.
  • the Lame curve is a rectangle.
  • Lame curve when 2 ⁇ , the Lame curve is a shape closer to a rectangle rather than an ellipse. Therefore, a dead space decreases, and the utilization efficiency of the element area is improved. For example, when 1 ⁇ 2, electric force lines can be more concentrated than the case of an ellipse.
  • a and b are parameters which determine the lengths of a short axis and a long axis, and as described above, it is preferable that a ⁇ b.
  • the outer peripheral shape of a transmission electrode will be described. As described above, it is preferable that the shape of a reception electrode and the shape of the inner periphery of a transmission electrode surrounding the reception electrode be elliptical. On the other hand, it is preferable that the outer peripheral shape of a transmission electrode be elliptical as illustrated in FIGS. 1A to 10 . For example, as illustrated in FIG. 13 , when a reception electrode 1303 of a capacitive sensor electrode 1300 has an elliptical shape and a transmission electrode 1302 thereof has a rectangular shape, a portion near a corner 1301 of the transmission electrode is more distant from the reception electrode than the other portions.
  • the percentage of electric force lines which are generated from the corner 1301 and are received in the reception electrode 1303 is low.
  • a shape not having the corner 1301 is preferable.
  • the above-described problem can be solved by setting the outer peripheral shape of a transmission electrode to be elliptical.
  • the outer peripheral shape of a transmission electrode is rectangular, it is preferable that the outer peripheral shape of a transmission electrode be rectangular.
  • the outer peripheral shape of a reception electrode is a Lame curve having a coefficient ⁇
  • the outer peripheral shape of a transmission electrode be a Lame curve having a coefficient close to a. That is, it is preferable that a reception electrode and the outer periphery of a transmission electrode have the same shape.
  • a transmission electrode be disposed so as to surround a reception electrode with a gap interposed between the transmission electrode and the reception electrode; it is preferable that a ratio of the width of the transmission electrode to the width of the reception electrode be within a range of 2 to 9; and it is preferable that the reception electrode have an elliptical shape and the outer peripheral shape of the transmission electrode also have an elliptical shape.
  • the capacitive sensor electrode 100 according to the first embodiment disclosed here is configured in consideration of the above-described conditions. Therefore, a change in capacitance is large when a detection object approaches the capacitive sensor electrode 100 , and the detection sensitivity is high.
  • a capacitive sensor in which the capacitive sensor electrode 100 according to the first embodiment disclosed here is used can achieve the excellent directivity and the improvement of the detection sensitivity at the same time.
  • the shapes of a transmission electrode and a reception electrode may be modified into various shapes other than the above-described shapes.
  • the shapes of a transmission electrode and a reception electrode may be vertically or horizontally asymmetric.
  • a capacitive sensor electrode includes a ground electrode that is disposed near a transmission electrode with a gap interposed between the transmission electrode and the ground electrode as in the case of the simulation models described above in FIGS. 10A to 10C .
  • the ground electrode is disposed near the transmission electrode, electric force lines spreading toward the vicinity of the capacitive sensor electrode are absorbed in the ground electrode and are not diffused to the vicinity of the capacitive sensor electrode.
  • a distribution of electric force lines generated from the transmission electrode changes and can prevent a problem of erroneous detection.
  • FIG. 14 illustrates a capacitive sensor electrode according to a third embodiment disclosed here.
  • FIG. 14 is a diagram illustrating a cross-section of the capacitive sensor electrode corresponding to the cross-section taken along IC-IC line of FIG. 1B ; and illustrating a modification example of the configuration of FIG. 1C .
  • a capacitive sensor electrode 1400 illustrated in FIG. 14 includes a transmission electrode 1402 and a reception electrode 1403 that are disposed on a principal surface of a substrate 1401 and further includes a ground electrode 1405 that is disposed on another principal surface (hereinafter referred to as “back surface”) opposite the principal surface.
  • back surface another principal surface
  • the ground electrode 1405 be disposed such that at least a part of the transmission electrode 1402 and the reception electrode 1403 is opposite the ground electrode 1405 with the substrate 1401 interposed between at least the part of the transmission electrode 1402 and the reception electrode 1403 and the ground electrode 1405 .
  • the ground electrode 1405 By disposing the ground electrode 1405 as described above, electric force lines moving from the transmission electrode 1402 to the reception electrode 1403 through the back surface side of the substrate are absorbed in the ground electrode 1405 , and the sensitivity in the back surface side direction of the substrate 101 significantly decreases. Accordingly, the capacitive sensor electrode 1400 is not likely to be affected by whether or not an object is present on the back surface side of the substrate 1401 , and the detection using the capacitive sensor electrode 1400 is stabilized.
  • the configuration according to the third embodiment disclosed here may be combined with the configuration according to the second embodiment in which the ground electrode is disposed near the transmission electrode.
  • a capacitive sensor including the capacitive sensor electrode 1400 according to the third embodiment disclosed here includes the ground electrode disposed on the back surface.
  • the detection sensitivity in the back surface side direction of the capacitive sensor electrode 1400 significantly decreases.
  • a decrease in the detection sensitivity on the back surface side caused by the ground electrode has a higher effect on a mutual capacitance type capacitive sensor than on a self-capacitance type.
  • the capacitive sensor electrode 1400 according to the third embodiment disclosed here is used for a mutual capacitance type capacitive sensor and thus can effectively decrease the detection sensitivity on the back surface side. Accordingly, the possibility of erroneous detection due to the above-described factors may be significantly reduced or prevented.
  • FIG. 15 is a plan view illustrating a capacitive sensor electrode according to a fourth embodiment disclosed here.
  • a capacitive sensor electrode 1500 illustrated in FIG. 15 has a structure in which two transmission electrodes 1502 are disposed on opposite sides of a reception electrode 1503 .
  • the transmission electrodes 1502 have the same potential and are connected to each other on wiring which is led out to a drive circuit of a sensor by a lead-out wiring (not illustrated). Even if the two divided transmission electrodes 1502 are provided, the same effects as those of the first to third embodiments disclosed here can be obtained as long as the two transmission electrodes 1502 are connected to have the same potential.
  • a capacitive sensor using the capacitive sensor electrode according to any one of the embodiments disclosed here can be suitably used as a non-contact switch for operating an opening and closing body such as a sliding door or a back door of a vehicle. Since the reception sensitivity is improved, the capacitive sensor according to any one of embodiments disclosed here can obtain sufficient sensitivity even if the surface thereof is coated and protected with a resin or the like, and can also be installed in an exterior member such as a sliding door of a vehicle. Further, since the capacitive sensor according to any one of embodiments disclosed here is a mutual capacitance type capacitive sensor, the detection range is limited to a position immediately above the sensor.
  • the capacitive sensor can also function to indicate a manufacturer or a car model or to indicate a non-contact switch.
  • An aspect of this disclosure provides a capacitive sensor electrode including: a first electrode that is disposed on a principal surface of a substrate; and a second electrode that is disposed on the principal surface to be distant from the first electrodes, in which the first electrode has a shape so as to be positioned on opposite sides of the second electrode.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that a ratio of the area of the first electrode to the area of the second electrode is 2 or more.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that at least a part of an outer peripheral shape of the second electrode is curved.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that at least a part of an outer peripheral shape of the second electrode is a part of a Lame curve defined by the following expression (1).
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that, in the expression (1), a ⁇ b.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that, in the expression (1), 1 ⁇ 2.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that, in the expression (1), ⁇ >2.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that at least a part of an outer peripheral shape of the first electrode is curved.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that at least a part of an outer peripheral shape of the first electrode is a part of a Lame curve defined by the following expression (1).
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that, in the expression (1), a ⁇ b.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that, in the expression (1), 1 ⁇ 2.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured such that, in the expression (1), ⁇ >2.
  • the capacitive sensor electrode according to the aspect of this disclosure may be configured to further include: a third electrode having a ground potential that is positioned on the principal surface of the substrate or on another principal surface opposite the principal surface.
  • the detection sensitivity can be improved.

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  • Theoretical Computer Science (AREA)
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  • Human Computer Interaction (AREA)
  • Switches That Are Operated By Magnetic Or Electric Fields (AREA)
  • Geophysics And Detection Of Objects (AREA)
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